1. Field of the Invention
The present invention relates to a rotatively driven type electric component with a slider actuated by screw drive.
2. Description of the Prior Art
With reference to FIGS. 9 and 10, description will now be directed to a conventional rotatively driven type electric component, which is a variable resistor driven by the rotation of a drive shaft.
FIG. 9 is a front view showing a variable resistor as a conventional rotatively driven type electric component and FIG. 10 is an exploded perspective view showing a movable portion of the variable resistor.
As shown in both figures, a casing 51 has a pair of support blocks 51a formed from a molding material and disposed opposite to each other.
A resistance board 52 is formed in the shape of a flat plate using an insulating material, with a resistor (not shown) being formed on the surface thereof, and the substrate 52 is mounted bridgewise between the support blocks 51a.
A drive shaft 53 is formed of a metallic material and has been subjected to a cutting work so as to have a screw portion 53a for operation and for drive and also have a support portion 53b. The drive shaft 53 extends in parallel with the resistance board 52 and is secured to the support blocks 51a of the casing 51. An end of the support portion 53b extends through one support block 51a and is projected to the exterior.
As shown in FIG. 10, the movable block 54 is formed in a generally rectangular shape with use of an electrically insulative material and it has a pair of generally rectangular lugs 60 formed on both side faces thereof, a groove 54a formed in an upper surface thereof and a cutout portion 54b formed in a lower surface thereof.
A slider 56 is formed in a general U shape by press working with use of a metallic plate having elasticity and has contact portions 57 at nearly central positions. Both end portions of the slider 56 are engaged with the cutout portion 54b of the movable block 54. The contact portions 57 of the slider 56 are in elastic contact with the resistor formed on the resistance board 52.
A holder member 55 is formed by bending a linear metallic material having elasticity and comprises a pair of generally U-shaped retaining portions 58 formed at both ends and a rectilinear connecting portion 59 which connects the retaining portions 58 with each other. The paired retaining portions 58 are brought into elastic engagement with the lugs 60 formed respectively on both side faces of the movable block 54 and the connecting portion 59 is fitted between adjacent threads of the screw portion 53a of the drive shaft 53 on the upper surface of the movable block 54 to transmit the rotation of the drive shaft 53 to the movable block 54, thereby causing the movable block 54 to move in an axial direction (longitudinal direction) of the drive shaft 53. With this movement of the movable block 54, the contact portions 57 of the slider 56 engaged with the movable block 54 come into sliding contact with an upper surface of the resistor, thus giving rise to an increase (or decrease) of resistance value. Since the retaining portions 58 and the connecting portion 59 are bent in different directions, the holder member 55 is complicated in its structure and hence machining for the holder member becomes complicated.
The following description is now provided about assembling the above rotatively driven type electric component.
First, the drive shaft 53 is mounted between the paired support blocks 51a of the casing 51 bridgewise and rotatably. Next, the slider 56 is brought into engagement with the cutout portion 54b of the movable block 54. Then, the groove 54a of the movable block 54 with the slider 56 locked thereto is brought into engagement with the screw portion 53a of the drive shaft 53 by means of a jig (not shown). In this state, the connecting portion 59 of the holder member 55 is fitted between adjacent threads of the screw portion 53a from above the mounted drive shaft 53, allowing the retaining portions 58 of the holder member 55 to come into engagement with the lugs 60 of the movable block 54.
Subsequently, the resistance board 52 is fixed to the support blocks 51a in parallel with the axis of the drive shaft 53. At this time, the resistance board 52 is mounted so that the resistor on the resistance board 52 is in elastic contactwith the contact portions 57 of the slider 56. Lastly, an upper opening of the casing 51 is closed and a frame (not shown) for holding the resistance board 52 is mounted.
In this way the assembly of the electric component is completed.
In the conventional rotatively driven type electric component, the holder member 55 for driving the movable block 54 is formed by bending a linear metallic material having elasticity and comprises a pair of generally U-shaped retaining portions 58 formed at both ends and a rectilinear connecting portion 59 which connects the retaining portions 58 with each other. The connecting portion 59 of the holder member 55 is fitted between adjacent threads located on the upper side of the screw portion 53a of the drive shaft 53, and the shaft is sandwiched between the holder member 55 and the movable block 54. Therefore, when the holder member 55 is to be mounted to the drive shaft 53 and the movable block 54, it is necessary that the drive shaft 53 and the movable block 54 be held simultaneously at predetermined relative positions by use of a jig or the like and holder member 55 then be brought into engagement with the lugs 60 against the resilience thereof. However, this is troublesome.
In addition, since this engagement is made from above the casing 51, it is necessary that an opening be formed in the casing, thus giving rise to the problem that an additional member such as a frame is required to block that opening.